Biodegradable lipids for delivery of nucleic acids

A compound according to formula I:

• or a pharmaceutically acceptable salt thereof,
• wherein:
• each instance of X is independently O or S;
• each instance of Y is independently O or S;
• each instance of R1 is independently hydrogen, optionally substituted alkyl, optionally substituted alkenyl, optionally substituted alkynyl, optionally substituted carbocyclyl, optionally substituted heterocyclyl, optionally substituted aryl, optionally substituted heteroaryl, halogen, —ORA1, —N(RA1)2, —SRA1, or a group of formula (iv):
• L is an optionally substituted alkylene, optionally substituted alkenylene, optionally substituted alkynylene, optionally substituted heteroalkylene, optionally substituted heteroalkenylene, optionally substituted heteroalkynylene, optionally substituted carbocyclylene, optionally substituted heterocyclylene, optionally substituted arylene, or optionally substituted heteroarylene, or combination thereof, and
• each of R6 and R7 is independently hydrogen, optionally substituted alkyl, optionally substituted alkenyl, optionally substituted alkynyl, optionally substituted carbocyclyl, optionally substituted heterocyclyl, optionally substituted aryl, optionally substituted heteroaryl, a nitrogen protecting group, or a group of formula (i), (ii) or (iii);
• formulae (i), (ii), and (iii) are:
• each instance of R′ is independently hydrogen or optionally substituted alkyl;
• X′ is O or S, or NRX;
• RX is hydrogen, optionally substituted alkyl, optionally substituted alkenyl, optionally substituted alkynyl, optionally substituted carbocyclyl, optionally substituted heterocyclyl, optionally substituted aryl, optionally substituted heteroaryl, or a nitrogen protecting group;
• Y′ is O, S, or NRY;
• RY is hydrogen, optionally substituted alkyl, optionally substituted alkenyl, optionally substituted alkynyl, optionally substituted carbocyclyl, optionally substituted heterocyclyl, optionally substituted aryl, optionally substituted heteroaryl, or a nitrogen protecting group;
• RP is hydrogen, optionally substituted alkyl, optionally substituted alkenyl, optionally substituted alkynyl, optionally substituted carbocyclyl, optionally substituted heterocyclyl, optionally substituted aryl, optionally substituted heteroaryl, an oxygen protecting group when attached to an oxygen atom, a sulfur protecting group when attached to a sulfur atom, or a nitrogen protecting group when attached to a nitrogen atom;
• RL is optionally substituted C1-50 alkyl, optionally substituted C2-50 alkenyl, optionally substituted C2-50 alkynyl, optionally substituted heteroC1-50 alkyl, optionally substituted heteroC2-50 alkenyl, optionally substituted heteroC2-50 alkynyl, or a polymer;
• and
• each occurrence of RA1 is independently hydrogen, optionally substituted alkyl, optionally substituted alkenyl, optionally substituted alkynyl, optionally substituted carbocyclyl, optionally substituted heterocyclyl, optionally substituted aryl, optionally substituted heteroaryl, an oxygen protecting group when attached to an oxygen atom, a sulfur protecting group when attached to an sulfur atom, a nitrogen protecting group when attached to a nitrogen atom, or two RA1 groups, together with the nitrogen atom to which they are attached, are joined to form an optionally substituted heterocyclic or optionally substituted heteroaryl ring.